The invention concerns a system for chassis control, specifically of passenger cars and trucks, and, more particularly, to a system for chassis control having a controlled loop and control parameters.
Essential for the design of the chassis of a motor vehicle is an efficient spring and/or shock absorber system. For one, it should make allowance for road safety and, for another, it is desirable to afford the passengers or a shock-sensitive cargo of the vehicle a maximally high travel comfort. From the vantage point of the spring and/or shock absorber system, these are conflicting objectives. With the chassis which today largely continue to be used, high travel comfort can be achieved through a maximally soft chassis adjustment, whereas with regard to high road safety a maximally hard chassis adjustment is desirable.
To resolve this conflict in objectives in designing a chassis, a changeover is made from the passive chassis which today largely continue to be used to adjustable, adaptive or, in a further step, to controllable, active or semiactive chassis. Depending on the predicted use of the vehicle, a passive chassis is laid out in the assembly either tendentially hard (sporty) or tendentially soft (comfortable). Any influence on the chassis characteristic is during the travel operation not possible with these systems. With adaptive chassis, the characteristic of the chassis can be changed during operation by a (normally stepwise) change of the shock absorber and/or spring values, depending on the situation of travel. The performance corresponds then at any adjustment momentarily to that of a passive chassis. As opposed to such passive, or adaptive, chassis, only active or semiactive chassis make it possible to effect simultaneously a high road safety and higher travel comfort. This is accomplished in that at any point in time there are optimal forces generated, for instance by active or semiactive shock absorbers, which derive from an algorithm as a result of measured or computed variables of movement of the vehicle. On such active or semiactive chassis, the characteristic of the suspension and/or shock absorber system can be influenced as well during the travel operation, depending on the state of travel, by adaptation of the parameters (amplifications, time constants, threshold values) or of the structure of the algorithm, with the resulting performance at any adjustment not necessarily corresponding to that of a passive vehicle. For instance, with active or semiactive chassis it is possible to attenuate various frequencies of movement at the same time differently in that, for instance, a skyhook damping, i.e., a damping of the vehicle body movements and/or a frequency-dependent damping of the wheel movements is incremented in the algorithm of control.
In the design of such active or semiactive chassis it is known, e.g., to arrange between the wheel units, or axles, and the vehicle body suspension systems parallel to shock absorber systems. An active shock absorber features for instance a cylinder which by means of a piston is subdivided in two working chambers. The properties of the shock absorber can be controlled by an active introduction or by draining of the pressure fluid, that is, a selective force can be applied between the wheel units and the vehicle body. As an alternative, it is possible with the so-called semiactive systems to vary the damping properties, for instance by the use of a bypass whose cross section is controllable. The piston, for example, may feature a valve whose passage cross section can be controlled. The so-called semiactive shock absorber systems are not actively acted upon by the pressure agent.
In a paper by W. Klinkner ("Adaptives Dampfungssystem ADS zur fahrbahn-und fahrzustandsabhangigen Steuerung von Dampfern einer Fahrzeugfederung" [Adaptive damping system ADS for road surface and state of travel dependent control of shock absorbers of a vehicle suspension], VDI Report No. 778, Dusseldorf, 1989). The shock absorber adjustments of an adaptive chassis are adapted in contingence on the static parameters describing the character of the road surface. For that purpose, the signals of a body sensor and of a wheel acceleration sensor are used. The paper proposes a conditioning of the captured road surface unevennesses, classified by frequencies, in various frequency ranges, for which purpose several filters of parallel arrangement are employed. Unfavorable on such a system is the high expense in view of, for one, the sensor engineering and, for another, in view of the filters. Furthermore, no optimal adaptation of this control system is possible to different states of travel.
A paper by D. Konik (Berechnung unbekannter Eingangssignale aus Messsignalen am Beispiel der Unebenheitsermittlung" [Computation of unknown input signals from measured signals on the example of unevenness determination], AT Automatisierungstechnik 39 (1991) 6 pages 205-210) deals with the computation of unknown input signals from the measured signals of a system. Here, the road profile is computed with the aid of signals representing the acceleration of the vehicle body and of signals representing the relative path between the vehicle body and the wheels, with the aid of an inverse system design.
WO 90/14240 (PCT/DE 90/00343) proposes a process for chassis control of vehicles where the chassis characteristic is changed in contingence on the longitudinal and transverse dynamics of the vehicle. This is accomplished by an appropriate variation of control parameters. The respective transfer function of the controller is adapted thereby to the longitudinal and transverse dynamics of the vehicle, so that with noncritical states of travel the greatest possible comfort exists, whereas at critical states of travel a tight chassis tuning applies which favors safety. With the system described here, however, a comprehensive optimization of control parameters to additional states of movement of the vehicle cannot be achieved.
In the publication "Computer controlled shocks smooth ride of GM luxury cars," Automotive News, Sep. 3, 1990, the hardest damping is adjusted for a chassis having damping properties of an adaptively adjustable design whenever great accelerations, hard braking or extensive steering angles are sensed. Describing the driving style of the operator, these parameters thus lead to a hard, sporty chassis adjustment. While thereby a limited adaptation of the chassis adjustment to the driving style of the operator is possible, a differentiated valuation of the effect of the driving style, in conjunction with other variables of influence on the state of travel of the vehicle, is not realized with this system.
Lastly, the article "Automotive Engineer," vol. 12, No. 6, December 1987, on page 40, right-hand column, lines 24 through 36, proposes a chassis control system where the changeover of the shock absorber parameters takes place in contingence on the vehicle speed and acceleration and steering maneuvers. Neither is with this system an optimum result obtainable with regard to chassis control, by the mere changeover of damping parameters.
The problem underlying the present invention is to design an active or semiactive chassis control system which allows for the various states of travel.